Fuel cells in general, and hydrogen fuel cells in particular, have received increased interest as possible power supplies for portable electronic devices. A fuel cell is an electrochemical device for continuously converting chemicals into direct-current electricity. A fuel cell typically includes two electrically conducting electrodes separated by an ionic-conducting electrolyte, and also any necessary systems for moving fuel into the cell or waste out of the cell. Fuel is continuously fed to one of the electrodes, where it is converted to an intermediate and travels through the electrolyte. A chemical that reacts with the fuel intermediate is fed to the other electrode. In a hydrogen fuel cell, hydrogen is fed to the anode, and oxygen is fed to the cathode. At the anode, the hydrogen is oxidized to H+ ions, which travel through the ionic-conducting electrolyte to the cathode. Electrons from the oxidation reaction travel through an external circuit to the cathode, thus powering a device connected to the fuel cell. At the cathode, the electrons reduce the oxygen, which then reacts with the hydrogen ions to form water as a waste product.
Fuel cells in general, and hydrogen fuel cells in particular, offer several advantages over the use of traditional batteries for portable electronic devices. For example, unlike batteries, a fuel cell produces electricity from fuels that are fed to the fuel cell only as needed. Therefore, the life of the fuel cell is theoretically unlimited, requiring only that the fuel supply be periodically replenished. Also, because hydrogen fuel cells produce water as a waste product, the use of fuel cells presents fewer environmental concerns than batteries, which generally contain hazardous chemicals such as heavy metals or acids.
While fuel cells may offer advantages over batteries for use with portable electronics, they may also present some problems. For example, the waste produced during operation of a hydrogen fuel cell must be disposed of or stored to prevent it from contaminating the electronic device or wetting a user. Also, the fuel supply should hold enough fuel to power the electronic device for an amount of time comparable to that possible with batteries. Finally, some fuel supplies may be unsuitably dangerous or expensive to use with a portable device. For example, compressed hydrogen gas may be explosive, and thus may present a danger to a user. Likewise, hydrogen liquid may be extremely expensive to produce and store, as it requires extremely low temperatures and special cryogenic storage containers.